The 37-year-old former England captain, who has joined the wealthy capital club on a five-month deal, replaced Javier Pastore in the 75th minute to the delight of a roaring home crowd.
Beckham, who sat on the bench after the packed stadium welcomed him as the sound system played The Beatles song "Hey Jude", immediately produced a trademark long pass to Ezequiel Lavezzi before joining in with a sterling defensive performance.
"He has brought his passing skills, his experience and tactical solutions," PSG coach Carlo Ancelotti told reporters.
"He only played 20 minutes tonight but he showed some good things."
Ligue 1 leaders PSG had opened the scoring thanks a bizarre Nicolas Nkoulou own goal in the 12th minute as the ball rolled into the net after Joey Barton and the Cameroon centre-back had both diverted a Lucas attempt.
The visiting team dominated possession and had the best chances throughout but Italy reserve keeper Sirigu made a string of superb saves to preserve the leaders' advantage until Zlatan Ibrahimovic sealed victory with the second goal from close range in stoppage time.
PSG have 54 points from 26 games, three ahead of Olympique Lyon, who beat Lorient 3-1 at home thanks to Lisandro Lopez, Rachid Ghezzal and Arnold Mvuemba's goals. Marseille stayed third on 46.
The hosts seemed started well and after two minutes Lucas hit the post following Ibrahimovic's back-heeled volleyed pass.
They were quickly rewarded with Nkoulou's own-goal but then let the visitors dominate possession, banking on in-form Ezequiel Lavezzi's pace to create chances.
Marseille struggled to unsettle their hosts' tough defence for half an hour, until Foued Kadir produced a fine solo effort down the right, only to see his powerful shoot parried away by Sirigu.
It was just the beginning of the show for the keeper who also pushed away efforts by Mathieu Valbuena and Andre-Pierre Gignac.
Marseille continued to push hard early in the second half but could not beat the inspired Sirigu who stopped Gignac's 61st-minute overhead kick and Andre Ayew's neat header.
The keeper should have taken all the plaudits but the crowd were focused on Beckham when the former Manchester United and Real Madrid player came on with 15 minutes left.
The 37-year-old was loudly cheered by the frozen fans following his trademark deep pass to Lavezzi who failed to make anything of it.
Playing in midfield, Beckham joined the team in the defensive work before Ibrahimovic sealed victory with the second goal.
In Lyon, the 20-year-old Rachid Ghezzal shone with his first league goal, which helped the home team keep PSG within reach thanks to a 3-1 victory.
Ghezzal tapped the ball in five minutes into the second half and Lyon wrapped up the win thanks to Arnold Mvuemba's last-gasp goal.
"I've waited for this goal for a long time now," winger Ghezzal told French channel beIN Sport
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